Ultrasound can be done at about 40 days of pregnancy, which is about 6 weeks, because at this time the initial development of the embryo can be observed and the results will be more accurate. If ultrasound is done in the first month of pregnancy, it is difficult to determine the development of the embryo. During the whole pregnancy, it is important not to do too many ultrasound examinations, it is best to limit them to 3-5 times. In early pregnancy, it is recommended to do only one ultrasound examination to confirm whether there is ectopic pregnancy or gravidity. During the 23-26 weeks of pregnancy, it is recommended to go to the hospital for a 4D ultrasound to check whether the fetus has any developmental abnormality, and an ultrasound in late pregnancy to check the placenta and amniotic fluid. Pregnant women need to hold urine before the ultrasound, especially in early pregnancy, holding urine will help the effect of the examination. Pregnant women should avoid excessive tension before and after the examination and keep a relaxed mood.